Supercircuits at the AMO/CM Interface

This research activity brings together AMO and CM techniques and perspectives to treat “supercircuits," electrical circuits of superconductors and mechanical circuits ofatomic gas superuids. We will couple ultracold atom clouds to superconducting circuits to explore coherence exchange and provide a new diagnostic of important quantum information (QI) issues. Superfluid gases configured as analogs to superconducting circuits, including Josephson tunnel junctions, will provide insight into supercircuits and the nature of superfluidity.

Illustration of how a Josephson junction would be introduced into a toroidal atom cloud. A sheet of light (green) is focused onto the atom cloud (yellow), which is trapped in a toroidal potential. This creates a tunnel barrier in the ring of atoms. Moving the sheet of light azimuthally around the ring creates, in the rotating frame, the equivalent of a magnetic field applied to an analogous superconducting circuit.

The advent of quantum atomic gases added a new macroscopic quantum system to superconductors and superfluid liquids. PFC research teams have expertise on macroscopic quantum phenomena in both CM and atomic gases, providing a natural platform for a center-based research effort to study both condensed and atomic gas supercircuits. By coupling atoms to superconducting circuits we can study the circuit behavior and improve the performance of both atoms and superconductors as carriers of quantum information. On the other hand, using our perspective on condensed matter superconductivity and superfluidity, we will study analogous phenomena in atomic gases. We will create circuits for the flow of atoms that are analogs of superconducting circuits, with a view to better understanding the nature of the analogies, the nature of each system, and possible new applications.

Among condensed matter qubits, Josephson junction (JJ) devices are one of the leading candidates because of long-lived Rabi oscillations, observation of entangled qubits and continual improvements in coherence times. Despite these remarkable advances, superconducting (SC) devices like SQUIDs (Superconducting QUantum Interference Devices) are bedeviled by loss and decoherence due to two-level fluctuators (TLFs), so coherence times are short. By contrast, atomic qubits with information stored in internal states have very long coherence times, but logic operations are slow [1]. We will lay the foundations for a hybrid QI approach, developing coupled atom-SQUID systems that can exploit the long coherence times of atomic systems for quantum memory and the fast, robust operations, control, and interconnectivity of SC qubits. We will also use these coupled atoms as unique probes to study the nature of the TLFs and perhaps help engineer better SC qubits. Transfer of QI from SC qubits to atoms may eventually allow a further connection to photons, yielding a SC qubit??photon coupling.

Another aspect of this major research activity explores the analogy between electrical circuits and atomic circuits. As in Josephson-junction-like structures for superfluid helium, that analogy is compelling but not exact. With atom analogs we expect both new perspectives on JJ circuits and the emergence of new research directions. While atom analogs of the Josephson effect have been realized in double-well potentials, there have so far been no experiments in which a tunnel barrier is introduced into a closed circuit of superfluid gas. Doing this will also present the opportunity to demonstrate some fundamental aspects of the nature of superfluidity.